It is well known that, for asphalt parking lots, a preventative maintenance treatment (typically an asphalt coating composition referred to as a “sealer”) will commonly be applied to the paving surface every 2-5 years or so. The coating material will typically be comprised of liquid asphalt or an anionic asphalt emulsion and will be applied using a wand sprayer or a spraying machine. The coating desirably operates to (a) seal the surface from water intrusion, (b) improve the appearance of the pavement, (c) protect the underlying asphalt pavement from oxidation and UV damage, (d) protect the pavement from oil and gasoline spills, and (e) provide a surface which is easier to sweep, clean, shovel, and maintain. All of these benefits increase the service life of the pavement.
Unfortunately, after curing, the micro-texture of the asphalt spray coatings heretofore known in the art has been much smoother than the micro-texture of the underlying pavement surface so that the frictional resistance offered by the asphalt spray coating has been significantly less than that of the underlying pavement. This reduction in frictional resistance is not a concern in low speed environments. However, because of this significant loss in surface frictional resistance, asphalt spray maintenance coatings of this type have not been applied to asphalt road surfaces or to other asphalt paving surfaces upon which vehicles will be traveling at higher speeds.
Moreover, no successful means of modifying and significantly increasing the micro-texture roughness and surface frictional resistance of the cured spray coating has heretofore been provided. Typical sealers are not formulated with a viscosity to suspend the typical aggregates chosen to enhance friction in other typical paving applications. The frictional aggregates used in other applications derive their frictional characteristics from both larger particles which cannot be sprayed and from material properties chosen with a maximum value of hardness and density.
Consequently, a need exists for an improved sprayable asphalt and aggregate coating composition which (a) will provide a significantly increase degree of surface micro-texture roughness when cured, (b) preferably will not have a lower surface micro-texture roughness than the underlying pavement to which it is applied, (c) can be spray-applied using conventional equipment, (d) will be highly durable, (e) will provide improved micro-texture over the life of the spray coating, (f) will provide all of the other benefits of a superior parking lot seal coating, and (g) can be pre-mixed, stored, and transported for later use.
The micro-texture roughness of an asphalt surface can be measured, for example, using a Dynamic Friction Test (DFT) as set forth in ASTM E 1911. This test provides a measure of surface friction as a function of sliding speed. The DFT apparatus consists of a horizontal spinning disk fitted with a spring-loaded rubber slider that contacts the paved surface as the rotational speed decreases due to the friction generated between the slider and the paved surface. The measured torque generated by the slider force is used to calculate a surface friction value as a function of speed.